Conventional diesel engines include an exhaust gas purification device in the exhaust passage, and the exhaust gas purification device includes a diesel particulate filter (DPF), which captures particulates contained in an exhaust gas, and an oxidation catalyst. Such an exhaust gas purification device treats an exhaust gas to raise the temperature in order to maintain the function of purifying an exhaust gas. The treatment regenerates the DPF by burning the particulates captured by the DPF and activates the oxidation catalyst. A burner that performs the treatment for raising the temperature of the exhaust gas is arranged upstream of the DPF and the oxidation catalyst.
One example of the structure of the burner is a multilayer tube structure. In the multilayer tube structure, a plurality of tubular members is overlapped to be coaxial. A burner having the multilayer tube structure is advantageous for saving space and raising the temperature of air for combustion.
For example, Patent Document 1 discloses a combustor that includes a combustion tube including an outer tube and an inner tube, a short auxiliary combustion tube arranged radially inside of the inner tube, and a vaporization tube arranged radially inside of the auxiliary combustion tube. The bottom of each tube is fixed to a base. When the combustor is activated, fuel is injected in the auxiliary combustion tube and is vaporized in a premixing region arranged in the auxiliary combustion tube. The vaporized fuel is mixed with air for combustion supplied from the vaporization tube. A flame occurs in a combustion chamber by igniting a premixed air-fuel mixture, in which the fuel and the air for combustion are mixed. In this way, the premixed air-fuel mixture is combusted. An air flow path, through which air for combustion passes, is provided between the inner and outer tubes. The air for combustion supplied to the flame promotes combustion.